This invention relates generally to magnetic recording media, and more particularly to patterned magnetic recording disks with discrete magnetic regions.
Conventional magnetic recording media, such as the magnetic recording disks in hard disk drives, typically use a granular ferromagnetic layer, such as a sputter-deposited cobalt-platinum (CoPt) alloy, as the recording medium. Each magnetized domain in the magnetic layer is comprised of many small magnetic grains. The transitions between magnetized domains represent the xe2x80x9cbitsxe2x80x9d of the recorded data. IBM""s U.S. Pat. Nos. 4,789,598 and 5,523,173 describe this type of conventional rigid magnetic recording disk.
The challenge of producing continuous granular films as magnetic media will grow with the trend toward higher areal storage densities. Reducing the size of the magnetic bits while maintaining a satisfactory signal-to-noise ratio, for example, requires decreasing the size of the grains. Unfortunately, significantly reducing the size of weakly magnetically coupled magnetic grains will make their magnetization unstable at normal operating temperatures. To postpone the arrival of this fundamental xe2x80x9csuperparamagneticxe2x80x9d limit and to avert other difficulties associated with extending continuous granular media, there has been renewed interest in patterned magnetic media.
With patterned media, the continuous granular magnetic film that covers the disk substrate is replaced by an array of spatially separated discrete magnetic regions or islands, each of which serves as a single magnetic bit. The primary approach for producing patterned media has been the use of lithographic processes to selectively deposit or remove magnetic material from a magnetic layer on the substrate so that magnetic regions are isolated from one another and surrounded by areas of nonmagnetic material. Examples of patterned magnetic media made with these types of lithographic processes are described in U.S. Pat. Nos. 5,587,223; 5,768,075 and 5,820,769.
From a manufacturing perspective, an undesirable aspect of the process for patterning media that requires the deposition or removal of material is that it requires potentially disruptive processing with the magnetic media in place. Processes required for the effective removal of resists and for the reliable lift-off of fine metal features over large areas can damage the material left behind and therefore lower production yields. Also, these processes must leave a surface that is clean enough so that the magnetic read/write head supported on the air-bearing slider of the disk drive can fly over the disk surface at very low flying heights, typically below 30 nanometers (nm).
An ion-irradiation patterning technique that avoids the selective deposition or removal of magnetic material, but uses a special type of perpendicular magnetic recording media, is described by Chappert et al, in xe2x80x9cPlanar patterned magnetic media obtained by ion irradiationxe2x80x9d, Science, Vol. 280, Jun. 19, 1998, pp. 1919-1922. In this technique Ptxe2x80x94Coxe2x80x94Pt multilayer sandwiches which exhibit perpendicular magnetocrystalline anisotropy are irradiated with ions through a lithographically patterned mask. The ions mix the Co and Pt atoms at the layer interfaces and reorient the easy axis of magnetization to be in-plane so that the irradiated regions no longer have perpendicular magnetocrystalline anisotropy.
IBM""s application Ser. No. 09/350,803, filed Jul. 9, 1999, now U.S. Pat. No. 6,331,364, describes an ion-irradiated patterned disk that uses a continuous magnetic film of a chemically-ordered Co (or Fe) and Pt (or Pd) alloy with a tetragonal crystalline structure. The ions cause disordering in the film and produce regions in the film that are low coercivity or magnetically xe2x80x9csoftxe2x80x9d and have no magnetocrystalline anisotropy.
A potential disadvantage of the Chappert et al. and IBM ion-irradiated patterned disks is that the regions separating the discrete magnetic regions from one another are not completely nonmagnetic, but still have some magnetic properties. Thus the magnetoresistive read head in the disk drive will detect noise and/or some type of signal from these regions. In addition, these ion irradiation techniques require the use of a mask that is difficult to fabricate because the holes in the mask are used to generate corresponding nonmagnetic regions on the disk, whereas it is desirable to use a mask that has the same hole pattern as the resulting magnetic bits on the disk.
What is needed is a patterned magnetic recording disk that has discrete magnetic regions separated by completely nonmagnetic regions so that only the magnetic regions contribute to the read signal, and that is made by a patterning technique where the mask pattern of holes matches the pattern of discrete magnetic regions of the disk.
The present invention is a magnetic recording disk that is patterned into discrete magnetic and nonmagnetic regions with the magnetic regions serving as the magnetic recording data bits. The magnetic recording layer comprises two ferromagnetic films separated by a nonferromagnetic spacer film. The spacer film material composition and thickness is selected such that the first and second ferromagnetic films are antiferromagnetically coupled across the spacer film. After this magnetic recording layer has been formed on the disk substrate, ions are irradiated onto it through a patterned mask. The ions disrupt the spacer film and thereby destroy the antiferromagnetic coupling between the two ferromagnetic films. As a result, in the regions of the magnetic recording layer that are ion-irradiated the first and second ferromagnetic films are essentially ferromagnetically coupled so that the magnetic moments from the ferromagnetic films are parallel and produce a magnetic moment that is essentially the sum of the moments from the two films. In the non-irradiated regions of the magnetic recording layer, the first and second ferromagnetic films remain antiferromagnetically coupled so that their magnetic moments are oriented antiparallel. The composition and thicknesses of the first and second ferromagnetic films are selected such that essentially no magnetic field is detectable at a predetermined distance above the magnetic recording layer corresponding to the height that the magnetic recording head would be located.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.